In some wireless networks, packets are fragmented and regrouped to generate a data segment that can be transmitted through the physical layer. Typically, the wireless communications device is made aware of the precise amount of data intended to be communicated in the segment when performing the fragmentation and grouping operations and thus may include information in a header indicating the precise amount of information being communicated by the segment.
In a wireless communications system including mobile nodes, channel conditions between a transmitter and receiver often vary over time. Different amounts of data can be reliably communicated in the same size transmission segment at different times depending upon the current channel conditions. In order to efficiently utilize the air link resources, it would be beneficial if a wireless communications device could delay its decision as to the data rate to be used for a transmission segment until as close as possible to the transmission, so that it can rely on the most current channel condition information. A wireless terminal typically relies on a determined data rate to be used in an upcoming segment when performing fragmentation and header generation operations. If a wireless terminal is to use a high data rate and communicate a large amount of data in a transmission segment, it may need a relatively large amount of time to perform the packet fragmentation and header generation operations. This processing time delay tends to push back the decision point for the data rate to use for the segment, and thus the decision as to which rate to use is being based on older, e.g., less reliable, channel condition information. To take into account potential variation in channel conditions from time of the selection of the rate to the time of actual transmission, one may lower an allowable data rate corresponding to a particular measured channel quality, which tends to lower throughput in the system.
Based on the above discussion there is a need for new methods and apparatus that support packet fragmentation and reconstruction, yet do not require the precise amount of data to be communicated in the segment to be known at the time at least some fragmentation and grouping operations are performed. It would be desirable if, in some embodiments, one or more header generation operations could be performed without knowing with certainty the amount of data which will be transmitted in a segment.